It’s among the most routine parts of modern presidential campaigning: a closing plug to visit a campaign website to donate or “find out more.”

And one by one, all of the candidates onstage Wednesday finished their closing statements at the end of the nearly three-hour Democratic debate by directing viewers to their websites.

All except former Vice President Joseph R. Biden Jr.

“If you agree with me, go to ‘Joe 30330' and help me in this fight,” Mr. Biden told viewers, hesitating as he worked his way through the numbers.

Of course, that is not a website. It appears Mr. Biden was trying to direct people to his campaign’s texting platform, which, according to his Twitter account, is engaged by texting “JOE” to the number 30330.