If you have a TextUs account with us you can access your own API key. This is required to connect with a few of our partners.
Access your Settings page by clicking the cog next to your name and number:
Now on the left-hand side of the page select API
Select API Key and then you can reveal your API key to copy and use where it is needed.
If you are an Organization Admin you will be able to view a list of API keys from your Account Overview page: