A Stripe or App Store key was refused

Stripe

• "Stripe says that key needs …" names the permission Stripe wants. Edit the key in Stripe, set it to Read, and connect again. The key itself does not change.
• "That key is allowed to …" means it can change something. Set every permission except Subscriptions and Prices to None.
• "That is a secret key" means a full secret key was pasted. Create a restricted key instead.

App Store

• "Apple refused those credentials" usually means one of the three identifiers is mistyped, or the key does not have the Sales or Finance role.
• "That does not look like the .p8 key file" means the key was not pasted whole. Open the file in a text editor and paste everything, including the BEGIN and END lines.