React Native issue : [Unhandled promise rejection: TypeError: f is not a function. (In 'f()', 'f' is undefined)]

I am trying to make a login system using states and fetch so that the user can receive his valid token and then put it in storage with Async Storage.I am still in the phase of communication with the API (expressjs). Everything works for the moment when I enter the email and the password I do receive the token in json but I have a warning type error which tells me:

[Unhandled promise rejection: TypeError: f is not a function. (In 'f()', 'f' is undefined)]

My code is very simple for the moment (I have absolutely no idea where it comes from):

const onSubmit = () => {    setLoading(true)    fetch('http://192.168.1.36:3000/api/users/login', {      method: 'POST',      headers: {        Accept: 'application/json','Content-Type': 'application/json'      },      body: JSON.stringify({        email: email,        password: password      })    })    .then((response) => response.json())    .then((res) => console.log(res))    .catch((err) => console.log(err))    .finally(setLoading(false));  }

I don't know if the syntax I use with fetch is "good" and "optimize" for a login system, but I hope I was clear enough in my explanation.

Tanks