If you have a Twitter Ads account, it’s possible to set up Lead Generation Cards that will automatically subscribe followers viewing this card to your TinyLetter account. Other viewers will be directed to your TinyLetter subscriber form.
To use this feature, you'll first need to connect your Twitter Ads account to TinyLetter. Once this is done, access the Lead Card within your Twitter account. Go to Data Settings and paste your TinyLetter URL into the Submit URL field.
This URL will be based off of your TinyLetter username in the following format: https://tinyletter.com/Username/twitter/lead
For example, if your TinyLetter username is "walterwhite" then this URL would be: https://tinyletter.com/walterwhite/twitter/lead
Once this URL is saved in the data settings, update the HTTP method to “POST” to point to your subscribe form. This can be done from the HTTP request menu in Twitter’s card settings. Next, complete the setup for your lead card in Twitter and you’ll be ready to publish.