Most business writing covers starting and growing. Almost none of it covers the week the money does not cover the salaries, or the morning you realise your partner has stopped contributing and you have nothing in writing.
So, plainly.
First, look at it honestly
Not at how it feels. At what is true. How much money is left. How long that lasts at the current rate. What would have to change for the business to be sound again.
Panic makes people act before they understand, and acting before you understand is how a difficult month becomes a closed business.
If you run out of money
The question is whether you have a real plan that would work if the business survived the gap.
If you do, taking on debt is a legitimate tool. Debt is not failure, it is a bridge, and businesses use it constantly. But be honest about whether it is a bridge or a hole. If the numbers say the debt would sink you rather than carry you, do not take it.
When debt is not the answer, sell part of what you own. Bring in an investor. Sell a share so the business has the money to come back to life.
Owning a smaller part of a business that lives is worth more than owning all of one that dies. Founders resist this out of pride far more often than out of arithmetic.
If the problem is a partner
Go back to what you agreed at the beginning. That is what the agreement is for.
If you never wrote it down, this is exactly where the trouble starts, and now you have two problems instead of one. Sit down and settle it properly. If you cannot, bring in a third person you both trust to judge between you.
Do not let it run. Disputes between partners destroy more businesses than competitors do.
And if you are reading this while things are fine, this is the moment to write it down. Who owns what share. Who decides what. What each of you actually does. How profit is split. What happens if one of you stops contributing, or wants to leave, or cannot continue. Who owns the name and the accounts. How you settle a disagreement.
Every one of those is easy to agree before there is money, and almost impossible after.
Plan for it before it happens
Keep some cash aside for bad times. Have a plan B you have actually thought about, rather than one you assume you would improvise.
And you do not always have to keep fighting
This is the part people find hardest to hear.
Sometimes the honest answer is that the business is not going to work, and continuing only spends more of your life on a decision you have already made.
Letting go is not the same as quitting. Half a loss is better than a whole loss, and a founder who closes one thing cleanly can start the next one with money, energy and a reputation intact.