Mobielnummer, e-mail, keuze, and bijzonderheden, are 4 fields not captured by the script because you have not inserted the relevant code. Then, you have configured the script to provide different error pages for every error, but you have only made a single error page (at least this is what you're saying here. Also, as you say, you only type in the name. If the other required fields are emty, the script must and will take you to the error page. But the whole problem is because you define the variable naam with uppercase capital letter (@$ Naam )
whilst in the script validation part you use lowercase capital letters : $naam so the script considers $Naam null and takes you to the error page.

Change also your email address as instructed above, and add the 4 lines necessary for the other 4 fields.

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