Another guided users on what to do “If the app stalls/freezes/locks up.”

“Close out of the app and log back in with your PIN,” the email read. “The app should save where you were. If it does not, please call in your results.”

Sarah Banks, a 39-year-old career adviser at Grinnell College, served as a caucus secretary, deputized by her precinct leader to record and submit results. She said she logged in to test the state party’s app Monday afternoon with no problem. But when it came time to report the actual tallies on Monday night, her app failed.

She spent the next four hours trying to phone in results.

“We had three of us call and we were all on hold,” Ms. Banks said. “When I was on hold for an hour, the phone disconnected.”

Shortly before 1 a.m., Ms. Banks said she was finally able to log in and plug in her precinct’s totals.

Mr. Grennan, the Poweshiek County chairman, said state party officials hadn’t introduced the app to his volunteers until days before Monday’s caucus. Some precinct leaders in his county were unable to properly enter a security code to download and access the app, let alone submit results.

“A lot of people were like, ‘I’m getting a virus on my phone’ and just quit it,” he said.

Ms. Truitt said the process was confusing for those who tried. It involved inputting a series of forms and links and security codes. Only one person at a precinct could be authorized to submit results through the app.