There have been several tickets where we observe all the mapping to be done rightly but still an error occurs with submission or sync.
This is with reference to ticket #92679.
For one customer the leads captured from their website were not syncing into LSQ.
On checking we noticed that there were multiple spaces between the letters in the submit option. < S U B M I T>
When we removed the spaces, the form worked fine and data got sent to LSQ.
Thus if there are issues despite of mapping done right, it is important that we check for the data that is posted and ensure that there are not any special characters involved so that it functions without any error.