Merchant's user could upload / update Merchant Public Key via 2C2P Merchant Portal.
go to ACCOUNT > Options
go to Payment Result URL and click EDIT
paste Merchant Public Key content in the text box and save.
2C2P Payment gateway will use this public key to encrypt any response messages to all of the Server-to-server API return URL.
Is there any issue if copied public key includes -----BEGIN CERTIFICATE----- and -----END CERTIFICATE-----?
There is no issue