How do I scale a Facebook campaign that is working?

There are two ways to scale a winning campaign, and neither is wrong.

1. Raise the budget. Any budget change can send the campaign back into the learning phase, for example going from $100 to $200 a day, so Facebook has to work out again who will convert and results can be weaker for a couple of days. To reduce that risk, some people raise the budget slowly, about 5 percent a day or 5 to 10 percent every few days. This may avoid the learning phase but is not guaranteed.
2. Duplicate. Use the Duplicate option on the working campaign or ad set, or create a new ad set aimed at a slightly different type of person. This doubles your budget without touching the one that works, and only the copy goes through learning. The copies can have some audience overlap and compete for the same people, but the audience is usually bigger than your budget, so it is rarely a problem.

If you can accept a few days of weaker results, just raise the budget. If you are very sensitive to the ad not working for a few days, duplicate.

Avoid changing a working ad itself, because it can stop working. Since Facebook's Andromeda update, each ad reaches almost its own segment of users, so a given ad or ad set eventually hits a limit. That is why adding new ad sets and new ads helps you grow.

The more you spend, the shorter the learning period, because learning ends after about 50 conversions. If your offer reaches 50 conversions in a day or two, re-entering learning matters less. A new campaign needs the same warm up time as the first one, and how many campaigns you run depends on your budget and how many conversions you can get in a week.