I did a signing for them 4/14/17. After a while, I started emailing them frequently about payment. For the last month, I have sent a reminder thru bill.com every day, in addition to emailing an overdue invoice every day to every email address I could find for them.
Occasionally I would get a response from someone making some excuse for non-payment, but mostly they just ignored me.
Finally, I received notice from bill.com that I will get my money on Monday - 154 days after signing.