Also make sure to create NEW subscription product after you change your API keys. You can’t use the subscriptions of your old account using the new API keys that you have entered.
For Security reasons, PayPal won’t let you create the subscription products using one account then switch to a different account. So make sure to delete the existing subscription products that you created with the old API keys. Then create NEW subscription products after you enter NEW API keys.
You can delete and create products from the “Products” menu of the plugin,