FME server: Some or all of the input parameters are invalid

My guess, and it’s only a guess without seeing logs or the fmw itself, is you have a defined one of your input parameters in Desktop/Form with a User Parameter type, which there are many:

Then in Server/Flow you have an input that doesn’t meet the parameter type configuration. For example if use the Number parameter type, set the configuration to between 1 and 99…. I cannot entered 100 in the Flow interface