In order to verify your amazon account you need to submit your amazon profile link, which is under your account→ see all account → your profile. Also this is only possible in a web browser not the app.
Method 1: Go to your account page directly (EASY)
STEP 1: Click on this link here
This link will take you directly to your account screen (if you are not logged in please do that first in your browser).
Step 2: Long press on the profile page and copy the URL.
STEP 3: Submit the link on the app
Method 2: Go to your account page from amazon home page (Hard)
STEP 1 : Open a Web Browser and visit Amazon
Note : This set of instructions work only in the browser and not in app.
STEP 2 : Log into your account and select 'View profile'
To view profile click on the 'Log in' icon.
Step 3 : Go to 'See all accounts' > 'Profile'
STEP 4 : Select any 1 review
STEP 5 : Long press on reviewer name to get the 'Copy Link' option
Tip: paste the copied link into another tab of the browser to know if the link works
STEP 6 : Paste the link and submit it on the OPA App.