Make sure you have a Video Asset File for the Main Video and optionally an HTML or Image Asset File for the End Card. Also make sure to have Tracker Asset as it is required.

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If you have your own VAST Code or VAST URL then End Card and Tracker Asset are ignored

Following are the relevant parameters to use with Create Creative API:

asset_file_id
end_card_id
end_time
name
rewarded_type
start_time
tracker_id
type: must be video

Guidelines for Managing Large Video Files (More Than 10MB)

If a video asset file is larger than 10MB, it will be automatically compressed. The video asset file cannot be used to create a creative until it has been compressed. Attempting to use it before compression will result in a validation error when calling the creative creation API.

To determine if the compression process is complete, check the processing field. If compression is in progress, the value will be:

"processing": {  
  "type": "mk_compress",  
  "status": "COMPRESSING",

If you try to create a creative at this moment, a validation error will occur.

Therefore, the logic for creating a video creative should be as follows:

Upload the file.
Create a video asset file.
Check the asset file API response
- If processing.type == 'mk_screenshot' || (processing.type == 'mk_compress' && processing.status == 'COMPLETE'),
  then create the creative.
- If processing.type == 'mk_compress' && processing.status == 'COMPRESSING',
  then wait two minutes, load the asset file, and repeat step 3.
- If processing.type == 'mk_compress' && processing.status == 'ERROR',
  then stop the script and contact support team or wait some time (an hour or more) and perform step 2 again - create asset file again.