Unable to send iMessage due to message blocking on T-Mobile

• Sign into your account at tmobile.com.
• Choose "Edit Profile Settings" at the top of the page
• Choose "Privacy"
• Choose "Block Scam Calls and Messages"
• Choose the line you are having trouble with and make sure all block options are disabled.

Don't go into a TMobile Store. Call their customer service. The folks in the store are salespeople. They will do everything they can to get a technical support customer out of the way so they can sell something to someone.

You do that using Safari on the t-mobile website. The upper right of their webpage has a pink My Account button where you can login to your account or create one if you have not done that. If you don't see the My Account button, there will be a button with 3 lines that when you tap it, you can choose the My Account option.

That way you can manage/view the account settings yourself, if you are reluctant to go through T-Mobile support.

I’ve had very good experiences with T-Mobile phone support. Someone picks up immediately most of the time. And I had a similar experience with a store, and when I complained (politely) when I called, the CSR checked and found that the added cost was a mistake of the salesperson and fixed it.