I have an inputfield with the variable name z_me5x_glacc to which I attach a local value help file. I have tried

LocalValueHelp F[z_me5x_glacc] domain="GLACCT"

but this results in a GuiXT error message "Screen element F[z_me5x_glacc] not found."

Don't use the internal variable name; please use the field label:

SAP://V[mymode]:1;OK:/nMM01