Hi Johnk,
As you have mentioned above, you are using the Adobe Sign Developer account.
Adobe Sign support team is tasked to handle post-sales support requests, it may be the reason they have directed you to the forums.
As informed, the settings are not enabled by default to access the Integration Key in the free Developer account.
I would recommend you to contact Pre-Sales team to get the settings enabled. They will be able to provide pre-sales technical assistance to you.
Please refer this link Subscription plans for eSign services | Adobe Document Cloud to get in contact with them.
Hope the information helps.
Let us know if you have any questions.
Regards,
Meenakshi