You need to create a customer lookup field then add it to the Opportunity entity.
Go to Settings > Customizations.
Select Customize the System.
Under Components, expand Entities, and then select the Opportunity entity.
Select Fields.
Click New.
Create the Billing Contact field.
Set the Field Requirement to Business Required.
Set the Data Type to Lookup.
For the Target Record Type select Contact.
Click Save and Close.
Click Publish All Customizations.
Open the Opportunities form.
In the Field Explorer drag the new field into the form.
Click Save
Click Publish

1 - Install the Power BI template app.
2 - Connect your Dynamics 365 Sale organization to the Power BI template app.
3 - Publish the application within your organization.

Explanation/Reference:
Perform Configuration
Testlet 3
Background
Bellows College has several sports teams. Sporting events take place throughout the year. Processes for managing and selling tickets to events are very outdated. The college uses Microsoft Excel to track who has paid for each private box seat for each season. The college uses a paper-based system to manage individual ticket sales. Bellows often loses money on ticket sales due to lack of accurate purchasing information.
The college currently does not support ticket sales on the day of a sporting event. All tickets must be purchased in advance.
Bellows College plans to streamline processes for selling tickets to sporting events. The organization needs an updated system that will support internal sales people and track all ticket sales for a season.
Sales team
Bellows College has inside phone sales representatives and regional sales representatives that are assigned to specific sales territories. Inside phones sales representatives primarily handle individual cash or credit card ticket sales. Regional sales representatives primarily handle group and private box sales. Phone inquiries for group and private box sales are entered into the system and assigned to the appropriate regional representative.
Dynamics 365
Bellows College has purchased Microsoft Dynamics 365 Sales to help manage their ticket sales. You are hired to configure the system to meet the college's needs.
The college has identified the following requirements for the new system:
* Enforce repeatable steps to promote and increase efficiency and consistency for ticket sales across all sports and venues.
* Calculate sales margins based on base ticket prices with discounts for group and alumni sales.
* Maximize private box sales.
* Provide visibility into all potential and pending sales.
* Track and report follow up activities performed by all sales representatives.
Current processes
Ticket sales
Ticket sales are completed and displayed based on the college's fiscal year which begins July 1 and ends June
30.
Ticket sales for existing customers will be entered as new opportunities for tracking and reporting purposes. To facilitate timely follow-up (and sales representative accountability), a phone call activity will be auto-generated every time a new opportunity is created.
Ticket sales for new customers will be entered in the solution as leads. Leads will have the following statuses:
Open, Qualified, and Disqualified. Status values cannot be customized. Status values cannot be customized.
Status reasons can be customized.
Ticket prices
The standard ticket price for all sporting events is $50. Non-alumni ticket purchases are priced based on the standard rate. Alumni ticket purchases are priced at the current cost. This season the current cost is $35 per ticket. All sports are priced on a markup, except for football. Football is priced based on a hard profit. The college has the following markup and margin policies for the three categories of ticket purchasers:

Ticket package discounts are available for group purchases. The following table shows pricing:

Private box seats
Because of the limited number of private box seats, private box seats sell out quickly. These seats are offered to current renters first, then alumni. Remaining box seat tickets are made available to others from year to year.
The dean of the college has expressed the desire to personally call the CEOs or primary decision makers of groups to thank them for renewing their private box rentals.
Private box sales for existing customers will be entered as opportunities and converted to orders when finalized. Private box and group sales for new customers will be entered as leads and will follow a standardized sales process. To support reporting, pending new customer sales will go through a verification process using the stages New, Pending Approval, Approved.
Requirements
Accounting
Budgets and taxes must be tracked over an annual accounting period. The name of the accounting period must be displayed based upon the July 1 date. The accounting period must support abbreviations and must be divisible into four quarters.
Invoices must include:
* Price List Products: Products tied to a price list
* Non-catalog Products: Existing products not part of the product catalog
* Opportunity Products: Products from a previously created opportunity
* Product prices on the invoice can be changed at the salesperson's discretion System configuration The system must be set up as follows:
* Individual cash and credit cards sales will be entered as orders in the system.
* New opportunities will automatically generate a required phone call activity for the assigned sales representative to be completed within 5 days. Valid outcomes of the call will be set to Connected, Left Message, and Wrong Number when closed.
* Non-renewals of private box rentals should be designated with the following outcomes for tracking and reporting purposes: Not interested, Budget cuts, No Longer in business, Other. If Other is chosen, the sales representative must provide additional information in the provided text box.
Tickets
The ticket manager must be able to create discounts for volume purchases of tickets for either groups or bundles of games.
The ticket manager must be able to calculate the best margins for ticket sales. They need to calculate prices as percentage of costs.
Reporting
The school's athletic director needs a fiscal year report that includes specific formatting based on a defined template. The report must contain a chart that displays the type of ticket purchaser (alumni, non-alumni, and student).
All sales reporting must be completed by using Dynamics 365 for Sales. Bellows College has purchased the online version of the Sales Content Pack for BI to allow for visualizations and the creation of dashboards for ticket sales. The sales team needs to use a secured connection to access the Bellows College Power BI dashboard.
Sales team members need the following report types to meet reporting needs:

Problem statements
The sales manager is concerned with the lack of sales from one of the sales representatives in comparison to the other sales representatives. The legacy system does not provide enough data to allow the manager to give proper feedback or guidance.
The sales manager has received emails from a potential private box customer named Contoso, Ltd. confirming that they have not had any contact from any sales representative even though they are ready to purchase group tickets.