App secret key length has increased
API
Effective January 28, 2020
The length of all newly generated Shopify app secret keys has increased from 32 to 38, adding a static prefix of shpss_, to make the secret keys easier to identify.
Existing API secrets will continue to function in their 32 character form until Shopify Partners manually regenerate them. This is the secret passed in as client_secret to https://{shop}.myshopify.com/admin/oauth/access_token to obtain an access token.
Learn more authenticating your Shopify app from the Shopify Help Center.