“Unable to assign the value "XX/XX/20XX" to the Schedule day of month field on the Gift. The value XX/XX/20XX is not a valid number which is expected for the Schedule day of month field. (in mapping Gift)”. This means that you have mapped a date field, but Raiser's Edge requires just the number of the day. There is a field setting at the end of the "Schedule day of month" field that will allow you to extract the day from the date.
You should also be aware that there is a difference between the date "X/X/20XX" and "XX/XX/20XX" for example if the incoming date is "2/6/2022" then then above date format will not extract the day. Instead you should use the option without leading zeros.
For those using EveryAction, please see this knowledgebase article for specific date format information.