The qualifications you need to teach Spanish will vary according to where you wish to teach; not just at what level, but through what medium and in what country. You will need to research requirements according to these variables, i.e. Private lessons, teaching online, teaching children/adults, teaching public school or college level.
For online tutorials, it can be enough that you are fluent or a native Spanish speaker, without the need for formal certification. If you are interested in seeing how this might work, check out two or three websites such as:
Success as a teacher with many of the online sites will depend on receiving positive student reviews. Acquiring students without a rating may be difficult initially, but tutors with a list of good reviews can command higher fees as that positive feedback accrues.
As a private tutor you could advertise to assist students through a recognized curriculum like Rosetta Stone, Pimsleur or another of the popular language programs. This type of teaching wouldn’t necessarily require credentials other than your native fluency and knowledge of Spanish or Latin culture.
Both online teaching and working as a private instructor have the advantage of allowing you to set your own hours to accommodate family, work and other commitments. Working from home is also seen by many as a desirable option; you have fewer expenses, no commute, no "work wardrobe”, no time clock, no boss.
In more formal settings such as teaching within the school system, qualifications to teach Spanish will include advanced certification such as a bachelor’s degree in Spanish education. Again, this may vary according to what country you intend to teach in.
Probably the best approach would be to contact the educational institutions you are hoping to work for, and determine their specific prerequisites, to ensure any training you undertake is in compliance with general standards for this level of teaching.