There are some reason that this may not be working.
1) This is not an acf field. Is this a field created by ACF? I’m only asking because it looks like a field for some type of eCommerce plugin.
2) Does this field exist and already have a value before you try to update it? update_field() will only work using the field name if the field already exists. If you are updating a post that does not already have this field then you need to use the field key rather than the field name. When using update_field() it is always better to use the field key and forget about using field names.
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