Hi @v-siky-msft thanks for your reply.
This is the peek code of my powerapps trigger :
{
"kind": "PowerApp",
"inputs": {
"schema": {
"type": "object",
"properties": {
"posttype_Value": {
"type": "string",
"description": "Enter initial value",
"isPartial": false
},
"Updatefileproperties_Id": {
"type": "integer",
"format": "int64",
"description": "Unique identifier of item to be updated",
"isPartial": false
},
"Updatefileproperties_Aan": {
"type": "string",
"isPartial": false
},
"Updatefileproperties_Afzender": {
"type": "string",
"isPartial": false
},
"Updatefileproperties_Verzenddatum": {
"type": "string",
"format": "date",
"isPartial": false
},
"Updatefileproperties_Emailbehandelaar": {
"type": "string",
"isPartial": false
},
"Updatefileproperties_Kenmerk": {
"type": "string",
"isPartial": false
},
"Updatefileproperties_Subject": {
"type": "string",
"isPartial": false
},
"Updatefileproperties_Internkenmerk": {
"type": "string",
"isPartial": false
},
"Updatefileproperties_AfzendendeOrganisatie": {
"type": "string",
"isPartial": false
},
"Updatefileproperties_BehandelaarID": {
"type": "string",
"isPartial": false
}
},
"required": [
"posttype_Value",
"Updatefileproperties_Id",
"Updatefileproperties_Aan",
"Updatefileproperties_Afzender",
"Updatefileproperties_Verzenddatum",
"Updatefileproperties_Emailbehandelaar",
"Updatefileproperties_Kenmerk",
"Updatefileproperties_Subject",
"Updatefileproperties_Internkenmerk",
"Updatefileproperties_AfzendendeOrganisatie",
"Updatefileproperties_BehandelaarID"
]
}
}
}
and this is how the verzenddatum is used in the flow (originally, i have also tried using compose and then putting the compose output in the update file properties block ; same result - the flow won't start)

Updatefileproperties_Verzenddatum was created by selecting 'ask in powerapps' in the orange circled field.
Keep in mind that I've already had contact with support about this issue twice where I am now at the point that this issue is being escalated to 2nd line support.