QGIS, MMQGIS, join by attribute function, cannot read the text(tab delimited file)

I am trying to join none spatial data with geographic data using the MMQGIS tool, on QGIS 3.14. However, I am running into an issue, when I try to carry out the function the MMQGIS tab will not let me select any fields for the Text(tab delimited) file. As such, I cannot carry out the function, due to the fact that I cannot select a field to match. It is worth noting when I import the text(tab delimited) file as a layer it works fine, I can see all the fields in the attributes table and all the data is there. Also note this is part of a course the the data set has been used by 100s of students, so it is unlikely that the data set is the issue.

I have tried using a CSV file in place of a text (tab delimited) file but to no success. It does let me select fields but only fields 1,2,3,4 and so on not the actual names of the fields, and the operation still fails. Please refer to the attached photo for further details, this should be easy as I am following a step by step tutorial and it still does not want to play ball.

I have tried it on to different computers one running QGIS v 3.10 and I have tried it on Qgis v2.8.

What should I do from here?