Well, the issue is the colourspace. That RGB colour isn’t reachable in the CMYK colourspace, so the software RIP (raster image processor) that processes the file for the CMYK printer that prints the shirt will map the RGB colour value to the closest point in the CMYK space. This is true of any RGB colour that’s outside of what CMYK can reproduce.
So . . . the expectations of the client have to be managed since there’s no technical way to make that colour on a CMYK printer. That’s why I sent that file. IF you were screen printing a few dozen shirts, we would mix a spot colour to match, but that’s not the case here.
If you’re not sure this short explanation is helpful, you can definitely search “effects of RGB to CMYk colourspace conversion” for more information. You might also want to see whether you can change the mode of the file to CMYK (we don’t use Canva, so can’t advise there) to see if you can alter the out-of-reach colours in the CMYK space to be something acceptable in line with the original design.