SIM800L Module Power Problem

I have a SIM800L module which connects to the network when I connect the VCC directly to the Li-Po’s + and Li-Po’s - to the GND with a wire. (Example 1) However, when I also use a cable, or breadboard to connect the VCC to the + (Example 2), it doesn’t connect and LED blinks with 1 second interval for around 10 times and it turns off for 3-4 seconds. Also when I connect the module to a FTDI adapter, it works with 2 cables for + and -.

Example 1

Example 2

What could be the issue and how can I solve it?

The datasheet states the unit needs 3.4-4.4V with 4v recommended. Maybe your battery voltage isn’t high enough. recharge it and try again. You should put a large bypass capacitor as the unit will need up to 2A in burst and maybe the current draw creates a dropout.

you know exactly the longer the wires get, the bigger the voltage drops

SIM800L needs to be as close as possible to power source

Obviously a power issue.
These things need peaks of about 2A when transmitting, the stray resistance of connections (especially on breadboard) can have a significant effect.

Is your module designed for 3.7V or 5V operation?

You should put a large bypass capacitor

The breakout board OP uses has one already: it's that yellow brick. That's a tantalum capacitor. Probably 470µF, maybe even more.

When I connect the battery to a voltmeter, it says 4.2V so the battery is full. Also when I connect an ammeter, it says the module draws 90 mA, but I think the battery can supply more current.

Also when I set a power supply to 4V and connect it to the module (with breadboard) it also doesn't work but the power supply can provide much bigger current than the peak of the module.

What do you get if you measure voltage at the SIM800L?

Here’s a trick. Try a 5v power source and put a diode on it.. it should drop about 0.7v. Rule out the battery.

Just make sure it can handle a couple amps