Did you try resetting your MP40 controller to default?
https://support.ecotechmarine.com/hc...ntroller-Reset
Once that is done go into ESL for your Reeflink and go to the Devices page. With your pump reset and plugged in click the "Add Devices Wirelessly" or something to that extent and wait until it finds it. You should have an "Unamed Device" in the left side list which you can click then click over on the "Add Here" link on the tank you want to add it too. Once it is in the list you should be able to rename it.
Make sure to click "Done" up top after you are done adding it to the tank to save the changes.
Hope this helps. Someone from Ecotech may have a better answer, this is just my best guess to give you something to try that should get you rollin' again.
I am with you, I still use my Reeflink for all my pumps and lights and don't want to get rid of it for a cell phone based platform! Call me and old fart but I like my desktop and browser based management vs using my phone for everything!