Tanzanian onlline visa

Is this the site you are using? https://eservices.immigration.go.tz/visa/start

My passport is stored away so could not do a test application, so did not get past this page. Presumably the issue you bring up is further along in the process?

It makes no sense that a visa would be valid at only some border crossings. ( but not everything works logically)

Yes, that is the site.

https://www.immigration.go.tz/index.php/en/services/visa-information

This is what concerned me.
https://eservices.immigration.go.tz/visa/guidelines

ENTRY PORTS:

Applicants whose visa applications have been approved are at present required to enter the United Republic of Tanzania through the five specified Entry Points, which are:

• Julius Nyerere International Airport (JNIA);
• Kilimanjaro International Airport (KIA);
• Abeid Amani Karume International Airport (AAKIA);
• Namanga border;
• Tunduma border.

At this point I have two suggestions, which may already occurred to you, so my apologies if I am redundant.

First is contact the authorities at the email listed where you found the restrictions and see if there is a way to get a Visa that would be accepted at that border crossing. The other is based on my presumption that you are going on safari as part of an organized tour, and that is to contact the tour company. They should know how to solve the seeming dilemma.

We crossed at Migori-Tarime from Kenya to Tanzania. We are Canadian so the process may be different. We could not get an on line visa and we did not wish to send our passport of to the Tanzanian embassy.

We landed on the Kenyan side, took a shuttle to the border. The shuttle bus had visa applications on board. They dropped us at the border, the shuttle bus driver helped through the process. Some people had visas, but they did not have any advantage. Make sure you have the exact change in US dollars. A different bus the drove us to the airport on the Tanzanian side.

It was a slow process, but relatively easy.

Enjoy your trip. For us it was a trip of the lifetime.

I have asked our travel agent about the visa and border crossing.

What is confusing is language about apply for visas at the Tanzanian embassy:

TO ALL VISA APPLICANTS

Kindly be informed that, from November 11, 2019 onwards Visa Services will no longer be issued at the Embassy of the United Republic of Tanzania in Washington D.C. For more information please click here.

All visa applicants are required to use new electronic system found at https://eservices.immigration.go.tz/visa/

Have you tried to call the embassy. You may get lucky and be able to speak to someone. Or try emailing on the chance that someone will reply.