Joint1 following error

You should have mentioned this is a RPI.
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When running the gcode file, set the Max Velocity slider to a lower value, till you do not get the joint following error anymore, then divide that value with 60 and set that value as the MAX_VELOCITY in the ini file.
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Also noted the scaling, if you have direct drive belts with GT2 20 tooth belts, the scaling should be 40 or 80 depending on drive microstepping.

Max_velocity in the ini file is in units per seconds (mm or inch), while everything in GUI is in units per minute, hence divide or multiply by 60.
The error you are getting is because you are requesting higher step rate than possible given the base period in use and timings for the software stepgens RPI uses, so you have to lower the step rate, or use less microstepping on the drives to get more velocity, but this will make more vibrations al low motor speeds. Still, do give it a try with microstepping at 4 and step scale.....
Step scale is motor steps per rotation multiplied by the microstepping value and divided by the pulley tooth/diameter/tooth pitch, in your case for a normal 1.8 degree per step motor that is 200 steps per rotation of the motor and pulley since it's directly driven, multiplied by 8 microsteping in the drives and divided by 20 tooth of the GT2 (GT2 is 2mm pitch between teeth) or 40mm
200*8=1600/40=40steps per mm for metric machine.
If you do set the drives to 4 microsteps, the scale in the ini file has to be changed to 20.