First of all, log into your Apple Developer account and then go onto App Store Connect.
In the top left hand corner, you'll have access to several different tiles. Select Agreements, Tax & Banking.
Next, make sure that the fields in all 4 tabs are filled out. Agreements, Tax, Banking & Contacts.
Now you've organised your Apple Developer account, log in to your Google Play Console.
On the left hand side you will see Settings - click here.
Next, click on Account details which will bring up your developer profile.
Then scroll down until you see Merchant Account, and follow the steps to set your account up as a merchant. Voila!